Within the scope of the invention, “cables” refer to tension-withstanding strands that are or become embedded in the conveyor belts as reinforcing cables and that are generally made of twisted wires or fibers. The cables extend longitudinally of the conveyor belt and are preferably steel cables. However, the invention also encompasses other types of cables, for example cables made of synthetic fibers or polymeric fibers (for example, aramid fibers or polypropylene fibers), carbon fibers, or mineral fibers.
In the course of making a conveyor belt, i.e. conveyor belts made of rubber with a cable core or a steel-cable core, a plurality of cables or steel cables is unwound from respective cable spools in a cable unwinding station, also referred to as the spool rack, and the individual cables are subsequently oriented so that they extend longitudinally of the belt and parallel to one another in a plane to form a “cable mat” that is then combined with the raw rubber webs in the combining device or coater. The cables are under a predefined tension during the combining and also during the subsequent pressing or vulcanizing.
In an apparatus known from DE 30 37 61 [U.S. Pat. No. 4,368,014] for making a conveyor belt having a steel-cable core of the type described above, a cable tensioner having a cable clamp is provided between the cable unwinder and the combining device, which in the cited document is referred to as a coating station. A clamping pull-through device is downstream of the vulcanizing press. The vulcanizing press is designed as a batch press, and the coater also operates cyclically. In the known device, the required tension of the steel cables is created with the aid of the cable tensioner, with the apparatus not in operation. After a conveyor belt section has been produced with the aid of the hot vulcanizing press, the press is opened, and with the cable tensioner relaxed and the cable clamp open, the conveyor belt is advanced by the length of the previously vulcanized section of conveyor belt by activating the pull-through device, and at the same time a corresponding length of the finished conveyor belt is wound up in the winding station, the next segment of the conveyor belt blank to be vulcanized is drawn into the heated vulcanizing press, the coating station is advanced by a corresponding path length toward the hot vulcanizing press, and the steel cable is appropriately tightened by the steel cable spools via pinion rollers. To remove any slack in the steel cables, the motor in the spool rack is subsequently activated so that the steel cable spools are driven opposite the steel cable pay-out direction. The cable clamp, which is integrated into the cable tensioner, is then closed, and all the steel cable sections present between the pull-through device and the cable clamp are tensioned with the aid of the cable tensioner. In this tensioned state the steel cables are then coated with the raw rubber. In this type of apparatus it is then necessary to relax the cables once again after the coating in order to transport the raw belt into the press, where the cables must be retensioned.
To achieve proper running of the manufactured conveyor belts during subsequent operation, a uniform distribution of tension in all embedded reinforcing cables is particularly important. For this reason, it has been proposed in DE 198 28 736 to associate a measuring device, which ascertains the cable tension, with each reinforcing cable, the measuring device being connected via a process computer to a control or regulating mechanism, and the control mechanism operating on the particular tensioning unit bearing the tension roller.
The apparatuses of the type described above that are known in practice have basically proven to be satisfactory, but are capable of further development.